Adjective

Translations

Steering is the term applied to the collection of
components, linkages, etc. which will allow for a vessel (ship, boat) or vehicle (car) to follow the desired
course. An exception is the case of rail
transport by which rail tracks
combined together with railroad
switches provide the steering function.

Introduction

The most conventional steering arrangement is
to turn the front wheels
using a hand–operated steering
wheel which is positioned in front of the driver, via the
steering
column, which may contain universal
joints to allow it to deviate somewhat from a straight line.
Other arrangements are sometimes found on different types of
vehicles, for example, a tiller or rear–wheel steering.
Tracked
vehicles such as tanks usually employ differential steering —
that is, the tracks are made to move at different speeds or even in
opposite directions to bring about a change of course.

Rack and pinion, recirculating ball, worm and sector

Many modern cars use rack and
pinion steering mechanisms, where the steering wheel turns the
pinion gear; the pinion moves the rack, which is a sort of linear
gear which meshes with the pinion, from side to side. This motion
applies steering torque
to the kingpins
of the steered wheels via tie rods and a
short lever arm called the
steering arm.

The rack and pinion design has the advantages of
a large degree of feedback and direct steering "feel"; it also does
not normally have any backlash,
or slack. A disadvantage is that it is not adjustable, so that when
it does wear and develop lash, the only cure is replacement.

Older designs often use the recirculating
ball mechanism, which is still found on trucks and utility
vehicles. This is a variation on the older worm and
sector design; the steering column turns a large screw (the
"worm
gear") which meshes with a sector of a gear, causing it to
rotate about its axis as the worm gear is turned; an arm attached
to the axis of the sector moves the pitman arm, which is connected
to the
steering linkage and thus steers the wheels. The recirculating
ball version of this apparatus reduces the considerable friction by
placing large ball bearings between the teeth of the worm and those
of the screw; at either end of the apparatus the balls exit from
between the two pieces into a channel internal to the box which
connects them with the other end of the apparatus, thus they are
"recirculated".

The recirculating ball mechanism has the
advantage of a much greater mechanical
advantage, so that it was found on larger, heavier vehicles
while the rack and pinion was originally limited to smaller and
lighter ones; due to the almost universal adoption of power
steering, however, this is no longer an important advantage,
leading to the increasing use of rack and pinion on newer cars. The
recirculating ball design also has a perceptible lash, or "dead
spot" on center, where a minute turn of the steering wheel in
either direction does not move the steering apparatus; this is
easily adjustable via a screw on the end of the steering box
to account for wear, but it cannot be entirely eliminated or the
mechanism begins to wear very rapidly. This design is still in use
in trucks and other large vehicles, where rapidity of steering and
direct feel are less important than robustness, maintainability,
and mechanical advantage. The much smaller degree of feedback with
this design can also sometimes be an advantage; drivers of vehicles
with rack and pinion steering can have their thumbs broken when a
front wheel hits a bump, causing the steering wheel to kick to one
side suddenly (leading to driving instructors telling students to
keep their thumbs on the front of the steering wheel, rather than
wrapping around the inside of the rim). This effect is even
stronger with a heavy vehicle like a truck; recirculating ball
steering prevents this degree of feedback, just as it prevents
desirable feedback under normal circumstances.

The steering linkage connecting the steering box
and the wheels usually conforms to a variation of
Ackermann steering geometry, to account for the fact that in a
turn, the inner wheel is actually traveling a path of smaller
radius than the outer wheel, so that the degree of toe
suitable for driving in a straight path is not suitable for
turns.

The worm and sector was an older design, used for
example in Willys and Chrysler vehicles, and the Ford Falcon
(1960's).

Power steering

As vehicles have become heavier and switched
to front
wheel drive, the effort to turn the steering wheel manually has
increased - often to the point where major physical exertion is
required. To alleviate this, auto makers
have developed power
steering systems. There are two types of power steering
systems—hydraulic and electric/electronic. There is also a
hydraulic-electric hybrid system possible.

A hydraulic power steering (HPS) uses hydraulic
pressure supplied by an engine-driven pump to assist the motion of
turning the steering wheel. Electric
power steering (EPS) is more efficient than the hydraulic power
steering, since the electric power steering motor only needs to
provide assistance when the steering wheel is turned, whereas the
hydraulic pump must run constantly. In EPS the assist level is
easily tunable to the vehicle type, road speed, and even driver
preference. An added benefit is the elimination of environmental
hazard posed by leakage and disposal of hydraulic power steering
fluid.

Speed Adjustable Steering

An outgrowth of power steering is
speed adjustable steering, where the steering is heavily assisted
at low speed and lightly assisted at high speed. The auto makers
perceive that motorists might need to make large steering inputs
while manoeuvering for parking, but not while traveling at high
speed. The first vehicle with this feature was the Citroën
SM with its Diravi layout,
although rather than altering the amount of assistance as in modern
power steering systems, it altered the pressure on a centring cam
which made the steering wheel try to "spring" back to the
straight-ahead position. Modern speed-adjustable power steering
systems reduce the pressure fed to the ram as the speed increases,
giving a more direct feel. This feature is gradually becoming
commonplace across all new vehicles.

Four-wheel steering

Four-wheel steering (or all wheel
steering) is a system employed by some vehicles to improve steering
response, increase vehicle stability while maneuvering at high
speed, or to decrease turning
radius at low speed.

In most active four-wheel steering systems, the
rear wheels are steered by a computer and actuators. The rear
wheels generally cannot turn as far as the front wheels. Some
systems, including Delphi's Quadrasteer and
the system in Honda's Prelude line, allow for the rear wheels to be
steered in the opposite direction as the front wheels during low
speeds. This allows the vehicle to turn in a significantly smaller
radius — sometimes critical for large trucks or
vehicles with trailers.

Many modern vehicles offer a form of passive rear
steering to counteract normal vehicle tendencies. For example,
Subaru used a passive steering system to correct for the rear
wheel's tendency to toe-out. On many vehicles, when cornering, the
rear wheels tend to steer slightly to the outside of a turn, which
can reduce stability. The passive steering system uses the lateral
forces generated in a turn (through suspension geometry) and the
bushings to correct this
tendency and steer the wheels slightly to the inside of the corner.
This improves the stability of the car, through the turn. This
effect is called compliance understeer and it, or its
opposite, is present on all suspensions. Typical methods of
achieving compliance understeer are to use a Watt's Link on a live
rear axle, or the use of toe control bushings on a twist beam
suspension. On an
independent rear suspension it is normally achieved by changing
the rates of the rubber bushings in the suspension. Some
suspensions will always have compliance oversteer due to geometry,
such as Hotchkiss live axles or a semi trailing arm IRS.

Recent application

In an active 4ws system all four wheels
turn at the same time when you steer. There can be controls to
switch off the rear steer and options to steer only the rear wheel
independent of the front wheels. At slow speeds (e.g. parking) the
rear wheels turn opposite of the front wheels, reducing the turning
radius by up to twenty-five percent, while at higher speeds both
front and rear wheels turn alike (electronically controlled), so
that the vehicle may change position with less yaw, enhancing
straight-line stability. The "Snaking effect" experienced during
motorway drives while
towing a caravan is
thus largely nullified. Four-wheel steering found its most
widespread use in monster
trucks, where maneuverability in small arenas is critical, and
it is also popular in large farm vehicles and trucks.

Previously, Honda had four-wheel
steering as an option in their 1987-2000Prelude,
and Mazda
also offered four-wheel steering on the 626 and
MX6 in
1988. Neither
system was very popular, in that whatever improvement they brought
to these already excellent-handling vehicles was offset by an
unavoidable decrease in sensitivity caused by the increased weight
and complexity.

A new "Active Drive" system is introduced on the
2008 version of the Renault
Laguna line. It was designed as one of several measures to
increase security and stability. The Active Drive should lower the
effects of under steer and decrease the chances of spinning by
diverting part of the G-forces generated in a turn from the front
to the rear tires. At low speeds the turning circle can be
tightened so parking and maneuvering is easier.

Articulated steering

Articulated steering is a system by
which a four-wheel drive vehicle is split into front and rear
halves which are connected by a vertical hinge. The front and rear
halves are connected with one or more hydraulic
cylinders that change the angle between the halves, including
the front and rear axles and wheels, thus steering the vehicle.
This system does not use steering arms, king pins, tie rods, etc.
as does four-wheel steering. If the vertical hinge is placed
equidistant between the two axles, it also eliminates the need for
a central differential,
as both front and rear axles will follow the same path, and thus
rotate at the same speed.

SuperSteer

SuperSteer is used by NewHolland to make
tractors turning radius smaller. The SuperSteer front axle
articulates when the wheels turn. The inside wheel moves away from
the frame, while the outside wheel moves in front of the
bumper/nose of the tractor, providing more tire clearance and a
greater turn angle. A picture of this turning action can be seen
here.

Steer-By-Wire

The aim of steer-by-wire
technology is to completely do away with as many mechanical
components (steering shaft, column, gear reduction mechanism, etc.)
as possible. Completely replacing conventional steering system with
steer-by-wire holds several advantages, such as:

The absence of steering column simplifies the car interior
design.

The absence of steering shaft, column and gear reduction
mechanism allows much better space utilization in the engine
compartment.

The steering mechanism can be designed and installed as a
modular unit.

Without mechanical connection between the steering wheel and
the road wheel, it is less likely that the impact of a frontal
crash will force the steering wheel to intrude into the driver's
survival space.

Steering system characteristics can easily and infinitely be
adjusted to optimize the steering response and feel.

As of 2007 there are no production cars available
that rely solely on steer-by-wire technology due to safety and
reliability concerns, but this technology has been demonstrated in
numerous concept
cars.

Safety

For safety reasons all modern cars feature a
collapsible steering column (energy absorbing steering column)
which will collapse in the event of a heavy frontal impact to avoid
excessive injuries to the driver. Non-collapsible steering columns
very often impaled drivers
in frontal crashes. Audi has a retractable
wheel system called procon-ten.